a(n) = (9*11^n - 1)/2.

Terms

a(0) =4a(1) =49a(2) =544a(3) =5989a(4) =65884a(5) =724729a(6) =7972024a(7) =87692269a(8) =964614964a(9) =10610764609a(10) =116718410704